This invention relates to an automatic door apparatus of the type operated by fluid pressure such as hydraulic or pneumatic pressure for opening or hermetically closing rooms or containers such as refrigerators, freezers, clean rooms or for depositories subject to radio wave noise, expecially large-sized commercial refrigerators or freezers.
In large-sized refrigerator or freezers, it is known to use electrically driven sliding doors adapted to slide along the side of the refrigerator panel for exposing or closing the front opening or aperture. The door is driven by an electric motor through a guide chain along a guide rail placed on the floor or along the upper edge of the front aperture and, when in the closed position, the door is tightly pressed against the refrigerator panel by means of suitable tightening units. The guide chains for electrically driven doors of large-sized refrigerators are heavy to move and noisy during operation. Also such door systems are expensive and complicated in structure. Further, since these doors are fully automatic in operation, a worker may be accidentally shut inside the refrigerator by the inadvertent operation or malfunction of the driving system.